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The different types of humidifiers are; Steam - they boil water and introduce it into the duct. Flow thu/bypass - they have a water panel the water drips onto, hot air from the furnance pass over the wet panel to evaporate water and introduce it into the duct. Drum - uses a wheel with a sponge material that rotates in standing water to make the warm air water contact. Nozzel trype - they spray atomized raw water into the duct. Self contained Room style - the type you buy at a hardware store.

Each has advantages/disadvantages.

Hope that helps

Outstanding - thank you.

I will be installing a bypass humdifier for my heat pump air handler in the very near future.

I suppliment the heat pump with a masonry wood burning fireplace w/insert. I get a lot of dry air due to the number of air exchanges caused by the fireplace.

The Aprilaire 700 is a flow thru, but it is not a bypass, its powered humidifier.
The Aprialaire 600, is both a flow thru and a by pass.
The Aprilaire 400, is a bypass, it is not a flow thru.
All three use pads.

On a heat pump, if you use a flow through, it will work better if you hook it to the hot water line.

And it doen't matter if you use a heat pump or gas furnace. Its the air infiltration(leaky house) that causes low humidity.

I don't care if the discharge air temp is 80 or 180°, it doesn't matter.
Its your house that needs sealed better.

The reason you take notice to the lower humidity when he aux is coming on. Is because, the humidity in the colder fresh air coming into your house is lower.

First of all I think this is an outstanding thread, and I thank the knowledgeable members for their informative posts.

Beenthere states above that air infiltration causes the low humidity. Most definitely true. I'd like to consider another potential source of air infiltration. Today's houses are generally built very tight. So tight that air exchangers (ERV/HRV'S) are installed to replace stale air during months of harsh weather when windows can't be opened to ventilate the home. It seems to me that this ventilation requirement potentially creates a problem of low RH%.

If we assume there is a limited amount of air infiltration, can the ventilation typically be scaled back such that it provides sufficient air exchanges without leaving the house in need of a humidifier?

Or is a humidifier required to meet both basic ventilation (home dependent) and humidity (30-50RH) requirements ?

My opinion thus far was that a steam humidifier can better handle this situation, mainly because the furnace does not need to run(just the fan) to distribute moisture. I know that it is possible to do this with a bypass humidifier but without the warm air the bypass is not very effective even when hooked to warm water. (please correct me if this is not true) My research thus far leads me to believe that the steam approach will be more costly to install and maintain then a bypass. I think there will be significant increase in the electric bill, what I don't know is whether there will be a savings in the gas bill to partially offset this.

I too have been researching humidifiers. I have a very tight 4,000sf home. HP with a Propane furnace that kicks in at 30F.

The Honeywell TrueSteam looked good, but 1500 watts is a big draw. $40 a month, as Zoneit suggested? That's as much as my hot tub.

Flow thru models obviously waste water - that just seems wrong this day and age. But how much actually goes down the drain on a given day?

I had a Desert Spring in my old house. It was a unique design that worked well, but that house was half the size.

Anyone have experience with the Triton 707 centrifugal? I like the idea of it's simplicity in design and installation.

"The Aprilaire 700 is a flow thru, but it is not a bypass, its powered humidifier.
The Aprialaire 600, is both a flow thru and a by pass.
The Aprilaire 400, is a bypass, it is not a flow thru."

Is there one that's powered but not a flow thru?

Thanks for letting me participate in this discussion.

As I have learned from beenthere, not all bypass humidifiers waste water. The 400A is a bypass humidifier but water does not flow through it, and therefore it does not have a drain. I looked into this type but decided that the extra filter changes and the potential for gunk build up was not for me. Just my opinion here, but the 400A is well suited for setups where a drain is not present or difficult to get to.

Edit: I forgot to mention that the truesteam also requires a yearly in-line filter change to make the 5 year warranty valid. I can't list the price for it per forum rules, but I can say it's a little more than a bypass filter would cost.

Not much room...

I just looked at my furnace. The return doesn't have much flat vertical surface area. One spot is real close to some joists - might work if I never want to finish that area. The other is at floor level, just before it hangs a left into the furnace.

1500 watts, is, and isn't a lot.
Thats 1500 watts in an hour of run time.

If it has to run for an hour at any outdoor temp, then either your house isn't as tight as you thing.
Or its too small for your house.

1500 watts can add better then &#189; a gallon of moisture to a home an hour.

On a 4000 sq ft home, with a .34 an hour air exchange, it would take about 40 minutes of run time for a 1500 watt steamer to add enough moisture to replace what is lost at an outdoor temp of 30&#176; at 40&#37; outdoor RH. To maintain an indoor 70&#176; 40 % RH.

1500 watts, is, and isn't a lot.
...
On a 4000 sq ft home, with a .34 an hour air exchange, it would take about 40 minutes of run time for a 1500 watt steamer to add enough moisture to replace what is lost at an outdoor temp of 30° at 40% outdoor RH. To maintain an indoor 70° 40 % RH.

OK, that's interesting. Say it does that 2x a day, that's about $5.00 a month at $0.12 a KWH. I could live with that. Would that be a reasonable expectation ?
Yes, my house is very tight. Although it's not Energy Star Certified, my building inspector showed me all of the ESC things they did (such as caulking between double studs at door jambs).
Still - how much water goes down the drain with a flow thru?

Finally Decided on my humidifier!

Yep, the decision is made. Based on the comments of many knowledgeable members here and my own calculations for air exchanges based on my energy report I have decided to go with the Truesteam. I got a few bids on installing a Truesteam vs the 600A and the 600A was about half. I think the cost will be more to operate the Truesteam unfortunately. The yearly in-line filter change will cost more than the yearly bypass filter change. I don't know how the utility bills would come out with the Truesteam or the Bypass but if I had to guess I think the bypass would probably be a little less expensive after natural gas, electric, and water are considered. The main reason I went with the Truesteam is because once I get my HRV under control, infiltration in my 4000sq/ft home will be limited and the on demand nature (meaning the furnace doesn't need to run) of the Truesteam should be able to complement my HRV.

So the net is, I'll have to pay more, install and maintenance, but I'll be able to control my humidity better with my IAQ zone panel and stats.

I like the Desert Spring. Depending on how hard you water is, you take the barrel out and soak it in vinegar or other mild acid solution every month to once a season. Uses basically a clock motor to turn it, so almost no electricity. I highly recommend installing an automatic drain that empties the pan once every 2 - 3 days, to keep the scuz out.
That being said, the output is not quite (or just barely) adequate for my 4,000 sq ft house. At my old house (2400 sq ft), it was perfect.

my thoughts on my Truesteam

I thought I would post my thoughts on my Truesteam after 2 days of usage. So far I am pleased with it. I am monitoring the number of flushes it does to determine how long it is running. (I have one of those KillaWatt devices and will plug that into it tomorrow). It flushes every 10 hours and in the first 2 days it ran a total of 5 hours per day. I have a 4000sq/ft house that is fairly tight. I keep the indoor temp between 68 and 70. The outdoor temp has ranged between 5 and 15 the last couple of days. And my indoor RH setting is 30. The first hour after I had it installed, I let it run continuously and it raised my indoor RH from 30 to 34. I verified this 15mins/1%RH the next day when I monitored it bringing the RH up from 29 to 30. Just for the record, my air exchanger is what keeps my RH down and not infiltration. When I don't run my air exchanger the house gets stale fast and you can smell last nights dinner in the morning and I can usually maintain humidity

I pay about 10.5 cents per kilowatt. The Truesteam takes 12 amps so 12Amps*120Volts = 1440Watts * 5 hours = 7.2Kw * 10.5cents = 75.6 cents/per day * 30 days = $22.58 per month. I didn't consider the water used because I think it is very minimal.

Figuring out how much a bypass would cost is a little harder. I'll take a guess since I don't know how much my water costs or how much my Natural gas costs off the top of my head. Lets assume its hooked to the warm water side of things to increase its efficiency. Most contractors I have talked to in my area suggest that be done. So here is my guess, I'd probably pay 5 to 10 bucks more in water usage since water is pretty cheap even if a lot is wasted. Natural gas to run the water heater more would probably cost 5 to 10 bucks a month more to. I'm not sure if the furnace blower fan would run more with a true steam or not so I'll just say that one is a wash. The install cost for the truesteam is roughly double that of a large bypass. The truesteam has an inline water filter that Honeywell recommends changing every year. I priced it out at around 20 bucks. Bypass humidifiers also have a filter that should be changed once a year too. I think they range from 15 to 20 bucks. The truesteam has a lot more parts to go bad then a bypass, so maintenance might be more in the long run.

All in all I like the performance of my truesteam, however I think it will cost me a little more in the long run to operate it.

My recommendation would be if you have a loose house and/or your furnace runs a lot then go with a bypass because it will take advantage of the furnace running. However if you have a tight house and/or your furnace doesn't run much (possibly oversized) then the Truesteam might be a better solution.

I pondered my humidifier selection for a long time, partly because the Truesteams weren't ready for last years heating season. Would I have been happy with a bypass model, hard to say for sure, but my guess is probably yes. I chose the Truesteam because I felt it had the best chance of meeting my humidification needs, and so far it has done that.